This invention pertains to the field of angiography. Angiography is the study of blood vessels with the use of x-rays while injecting an iodine-based or other fluid (contrast media) into the body through a catheter situated in a blood vessel. An angiographic injector is an apparatus which controls the delivery rate, amount, and maximum pressure of the fluid being injected.
There are many angiographic injectors on the market today, and each suffers from its own characteristic drawbacks and deficiencies. A few are noted in the paragraphs to follow.
A bothersome and time-consuming operation necessary in the use of all known injectors is that of exchanging an empty syringe cartridge with a filled one. Known injectors necessitate a certain degree of mechanical disassembly, be it unscrewing a collar, turning a handle to remove a subassembly, or a similar maneuver to gain access to the empty syringe cartridge. Once a fresh cartridge is in position, the reverse operation of mechanical assembly must be carried out before the injector is ready for another injection.
It is known to elevate the temperature of the contrast media to that of the body prior to injection. It is also known that if the contrast media is injected at a temperature above approximately 106.degree. F, damage to the brain may occur. Though attempts have been made to ensure that the temperature of the contrast media is maintained below the critical 106.degree. F, none has been totally satisfactory.
Known angiographic equipment have incorporated indicators to show when the injector is ready to inject. The indicators, however, maintain the same state for readiness and injection. Therefore, while the operator is readily able to discriminate between disarmed and readiness, it is difficult to discriminate between readiness and injection.
Another drawback of prior equipment relates to the controls for filling syringes by using the injector. Such controls traditionally drive the plunger of the injector at a constant rate, and hence the filling operation cannot be conducted at maximum efficiency.
The volume of contrast media to be delivered depends upon settings manually introduced to the apparatus. With a single injection, the syringe is filled to the volume required, or higher, and the volume control is set to the desired volume of injection. However, if several injections are to be made from the same syringe, the amount of fluid remaining in the syringe for any given injection may be less than that required for injection. Such a condition of insufficient syringe volume cannot be detected in known angiographic injectors.
Known flow controlled injectors using servo feedback systems, adjust the injection pressure to deliver the contrast media at the desired and set injection rate. Occasionally there may be insufficient pressure, resulting in an underrate injection. Such an underrate injection will go unnoticed in injectors on the market today.
Several injectors available today are equipped with a mechanism for controlling equipment auxiliary to the injector system, particularly film changers or film changer programmers used in conjunction with the injector system. Typically, a film sequence is initiated by a switch closure in the injector itself, completing a circuit within the auxiliary equipment. Though it is desireable to synchronize the changing of the film in the film changer with the injection contrast media into the vascular system, there are no effective R-wave synchronism capabilities in presently available angiographic injectors.
Also important is that the operator be capable of accurately planning an injection sequence. And since cardiac injections are customarily carried out in pulses, spaced so as to synchronize with the ECG, it would be helpful for the operator to have a visual display of the patient's cardiac activity. Yet no known injectors provide a mechanism for displaying the pertinent cardiac activity to enable the operator to accurately map out an injection program.
Nor does any known angiographic injector have the ability to preview injection parameters displayed with respect to the ECG. That is, there is no present capability for visually inspecting the pre-set injection parameters prior to an actual injection in order to determine if all parameters are properly set. Similarly, there are no known injectors which visually display the entire injection sequence as it was actually carried out.
An important drawback of today's injectors is that a high-pressure injection can be initiated prior to the completion of the entry of injection parameters, or in the event that a parameter has been inadvertently changed. There are some safety features on known equipment, but none sophisticated enough to ensure a high degree of safety.
Conventional motor systems for controlling the injection of contrast media have been plagued by runaway or burned motors, or other similar detrimental failures in the motor control system. Numerous safety features, including fuses, circuit breakers, brakes, crowbar circuits, current limiting circuits, and over-current detecting circuits have been incorporated. But the known injectors have still failed to provide inherent safety from the types of failures described above.
The flow of blood varies in different portions of the body and even in different portions of the heart cycle. This creates a problem in angiography, because vessel opacification is a function not only of injection rate, but also of blood flow rate. Accordingly, there is a need to have the capability of programming variable injection rates in an angiographic injector. In this regard, U.S. Pat. No. 3,812,843 describes stepping to new injection rate values in a time sequence in order to build a programmed injection function. However, only this stepped sequence is disclosed in the programming of variable injection flow rates.
Another serious problem in conventional angiographic equipment relates to the injection of air into the vascular system. There have already been deaths caused by the initiation of injections with empty syringes. A need obviously exists for a mechanism whereby the presence of an empty or an only partially filled syringe can be detected prior to injection.
There is also the need in angiography for improvements in both disposable and media-containing syringe cartridges. In particular, today's syringes suffer from serious drawbacks with respect to sterility. They are frequently not pre-sterilized to satisfaction prior to an injection. A need also exists for syringe cartridges which may readily be associated with an angiographic injector without unduly stressing the injector or the cartridge itself.
Especially common with respect to disposable syringe cartridges is the problem of syringe capacity changes which result during high-pressure injections. When the cartridge assembly is subjected to the injection pressures, the cartridge swells and hence the initial injection rate is decreased. Similarly, when the injection pressure is reduced at the end of the injection, the cartridge deflates, and hence injection of contrast media continues when none is desired. No known injectors in any way compensate for this change of syringe capacity due to the application of injection pressures.
Other problems and drawbacks are common to the angiographic injectors known today. Among these are the complexity of the apparatus necessary to develop electrical indications of parameters such as the actual pressure developed at the tip of the syringe during an injection, and the difficulty encountered by servicemen in pinpointing the location of problems should they occur in the equipment. Furthermore, known angiographic injectors are generally lacking in the capability of being remotely controlled, and employ panel elements which are susceptible to the accumulation of fluids and dust.
It is the purpose of the present invention to cure each of the drawbacks and disadvantages of known angiographic injectors discussed in the preceding paragraphs.